Structural tubular products have a wide range of applications. Some examples include construction and architectural applications, structural components for vehicles and industrial equipment, and transmission towers, highway guardrails, light posts and other structures. Tubular components can often combine strength with significant weight and material reduction.
One application of such tubular products is axle housing assemblies. Typically, such axle housing assemblies include an axle housing and other components such as brake flanges or spiders, spring seats, shock absorber pads, among others. The axle housing has an axle housing tube (which encloses the axle shaft) and a spindle located at the terminal ends of the axle tube (for engaging the wheel or bearing parts).
Typically, different parts of an axle housing have different load or strength requirements. Accordingly, these parts have different internal or external diameters and wall thickness, optimized for each part to meet the structural requirements and to reduce weight. Generally, all of the aforementioned parts are formed separately and subsequently welded together to form the axle housing. However, the various forming and welding steps are time and labour intensive, and also tend to introduce some undesirable side-effects, especially at the locations of weld.
For example, as is known in the art, axle spindles generally require a larger wall thickness than the axle tube due to the increased strength demands. As such, it is common for the spindles to be forged separately and subsequently attached (by such means as friction welding) to the axle tube. Examples of such a two-step method are taught in U.S. Pat. Nos. 3,837,205 and 6,279,695. However, as indicated above, the requirement for welding increases the cost of the final article. Moreover, due to the high temperatures generated and required by the known welding methods, the strength of the metal surrounding the welded regions are known to be reduced.
U.S. Pat. No. 4,435,972 teaches a multi-step method for forming an axle housing that uses a series of mandrels to form the required cross sectional profile. This method is limited to tubes with a uniform external diameter, with internal diameters varied along the length of the axle housing to provide the desired cross sectional profile. Further, this method is limited to forming tubes made of steel having high formability characteristics and could not be used to form heavy duty axles housings.
Therefore there is a need for developing a new design for tubular products that will contribute to overall weight reduction while increasing durability and load bearing capability. It is an object of the present invention to mitigate or obviate at least one of the above mentioned disadvantages.